Optical circulator for dispersion compensation

Abstract

Dispersion compensation is achieved in an optical communications system by using an optical circulator with first, second, and third ports. The first and third ports are connected to system optical fibers. The second port is connected to a dispersion compensating fiber and return means. The signal passes through the dispersion compensating fiber twice permitting shorter dispersion compensating fibers to be used than were previously used. A Faraday rotator may be used compensate for the polarization mode dispersion of the fiber.

We claim: 
     
       1. An optical communications system comprising: a first transmitter;   a first receiver;   first and second optical fibers connected to said first transmitter and said first receiver, respectively;   an optical circulator having at least first, second, and third ports, said first and third ports connected to said first and said second optical fibers, respectively;   a first dispersion compensating waveguide connected to said second port; and   first return means connected to said first dispersion compensating waveguide, said returns means returning a signal to said circulator through said dispersion compensating waveguide.   
     
     
       2. An optical communications system as recited in claim 1 in which first said return means comprises reflecting means. 
     
     
       3. An optical communications system as recited in claim 1 in which said first return means comprises a grating. 
     
     
       4. An optical communications system as recited in claim 1 in which said first return means comprises an optical circulator having at least first, second, and third ports, and an optical fiber; said first port being connected to said first dispersion compensating waveguide, and said optical fiber being connected to said second and said third ports. 
     
     
       5. An optical communications system as recited in claim 1 further a pump laser, a multiplexer, and a fiber amplifier, said pump laser being connected to said multiplexer, and fiber amplifier being connected between said return means and said second port of said circulator, said multiplexer being connected to said first port when said fiber amplifier is connected to said second port and to said second port when said fiber amplifier is connected to said multiplexer. 
     
     
       6. An optical communications system as recited in claim 1 in which said optical circulator has a fourth port. 
     
     
       7. An optical communications system as recited in claim 6 further comprising a second transmitter and a second receiver; said second transmitter being connected to said second optical fiber and said second receiver being connected to said first optical fiber. 
     
     
       8. An optical communications system as recited in claim 7 further comprising second return means and a second dispersion compensating waveguide; said second dispersion compensating waveguide being connected to said second return means and to said fourth port. 
     
     
       9. An optical communications system as recited in claim 1 further comprising a Faraday rotator connected to said dispersion compensating waveguide and said return means. 
     
     
       10. An optical communications system as recited in claim 1 further comprising a preamplifier connected between said optical circulator and said transmitter. 
     
     
       11. An optical communications system as recited in claim 10 further comprising a light source in said transmitter for pumping said preamplifier. 
     
     
       12. An optical communications system as recited in claim 1 further comprising an amplifier connected between said optical circulator and said receiver. 
     
     
       13. An optical communications system as recited in claim 12 in which said amplifier is remotely pumped by a light source in said receiver. 
     
     
       14. Apparatus comprising: an optical circulator having at least first, second, and third ports;   return means; and   a first dispersion compensating waveguide, said waveguide being connected to said return means and to said second port, said returns means returning a signal to said circulator through said dispersion compensating waveguide.   
     
     
       15. Apparatus as recited in claim 14 further comprising: a pump laser;   a multiplexer; and   a fiber amplifier, said pump laser being connected to said multiplexer, and fiber amplifier being connect between said return means and said second port of said circulator, said multiplexer being connected to said first port when said fiber amplifier is connected to said second port and to said second port when said fiber amplifier is connected to said multiplexer.   
     
     
       16. Apparatus as recited in claim 14 in which said return means comprises reflecting means. 
     
     
       17. Apparatus as recited in claim 14 in which said return means comprises a grating. 
     
     
       18. Apparatus as recited in claim 14 in which said return means comprises a circulator having first, second, and third ports; and an optical fiber, said first port being connected to said dispersion compensating waveguide, and said optical fiber being connected to said second and said third ports. 
     
     
       19. Apparatus as recited in claim 14 in which said optical circulator has a fourth port. 
     
     
       20. Apparatus as recited in claim 17 further comprising a second return means, and a second dispersion compensating waveguide, said second dispersion compensating waveguide being connected to said second return means and to said fourth port. 
     
     
       21. Apparatus as recited in claim 14 further comprising a Faraday rotator connected to said dispersion compensating waveguide and to said return means.